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Add a function to extract the pages from a user-space supplied iterator
(UBUF- or IOVEC-type) into a BVEC-type iterator, retaining the pages by
getting a pin on them (as FOLL_PIN) as we go.
This is useful in three situations:
(1) A userspace thread may have a sibling that unmaps or remaps the
process's VM during the operation, changing the assignment of the
pages and potentially causing an error. Retaining the pages keeps
some pages around, even if this occurs; futher, we find out at the
point of extraction if EFAULT is going to be incurred.
(2) Pages might get swapped out/discarded if not retained, so we want to
retain them to avoid the reload causing a deadlock due to a DIO
from/to an mmapped region on the same file.
(3) The iterator may get passed to sendmsg() by the filesystem. If a
fault occurs, we may get a short write to a TCP stream that's then
tricky to recover from.
We don't deal with other types of iterator here, leaving it to other
mechanisms to retain the pages (eg. PG_locked, PG_writeback and the pipe
lock).
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: Steve French <sfrench@samba.org>
cc: Shyam Prasad N <nspmangalore@gmail.com>
cc: Rohith Surabattula <rohiths.msft@gmail.com>
cc: linux-cachefs@redhat.com
cc: linux-cifs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>
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Split some core bits out into their own file. More bits will be added to
this file later.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/164623006934.3564931.17932680017894039748.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/164678218407.1200972.1731208226140990280.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/164692920944.2099075.11990502173226013856.stgit@warthog.procyon.org.uk/ # v3
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Split fs/netfs/read_helper.c into two pieces, one to deal with buffered
writes and one to deal with the I/O mechanism.
Changes
=======
ver #2)
- Add kdoc reference to new file.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/164623005586.3564931.6149556072728481767.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/164678217075.1200972.5101072043126828757.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/164692919953.2099075.7156989585513833046.stgit@warthog.procyon.org.uk/ # v3
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Rename the read_helper.c file to io.c before splitting out the buffered
read functions and some other bits.
Changes
=======
ver #2)
- Rename read_helper.c before splitting.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/164678216109.1200972.16567696909952495832.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/164692918076.2099075.8120961172717347610.stgit@warthog.procyon.org.uk/ # v3
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Split netfs_io_* object handling out into a file that's going to contain
object allocation, get and put routines.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/164622995118.3564931.6089530629052064470.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/164678197044.1200972.11511937252083343775.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/164692894693.2099075.7831091294248735173.stgit@warthog.procyon.org.uk/ # v3
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Gather statistics from the netfs interface that can be exported through a
seqfile. This is intended to be called by a later patch when viewing
/proc/fs/fscache/stats.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-and-tested-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Dave Wysochanski <dwysocha@redhat.com>
Tested-By: Marc Dionne <marc.dionne@auristor.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: linux-mm@kvack.org
cc: linux-cachefs@redhat.com
cc: linux-afs@lists.infradead.org
cc: linux-nfs@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: ceph-devel@vger.kernel.org
cc: v9fs-developer@lists.sourceforge.net
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/161118139247.1232039.10556850937548511068.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161161034669.2537118.2761232524997091480.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161340397101.1303470.17581910581108378458.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/161539539959.286939.6794352576462965914.stgit@warthog.procyon.org.uk/ # v4
Link: https://lore.kernel.org/r/161653797700.2770958.5801990354413178228.stgit@warthog.procyon.org.uk/ # v5
Link: https://lore.kernel.org/r/161789079281.6155.17141344853277186500.stgit@warthog.procyon.org.uk/ # v6
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Add a pair of helper functions:
(*) netfs_readahead()
(*) netfs_readpage()
to do the work of handling a readahead or a readpage, where the page(s)
that form part of the request may be split between the local cache, the
server or just require clearing, and may be single pages and transparent
huge pages. This is all handled within the helper.
Note that while both will read from the cache if there is data present,
only netfs_readahead() will expand the request beyond what it was asked to
do, and only netfs_readahead() will write back to the cache.
netfs_readpage(), on the other hand, is synchronous and only fetches the
page (which might be a THP) it is asked for.
The netfs gives the helper parameters from the VM, the cache cookie it
wants to use (or NULL) and a table of operations (only one of which is
mandatory):
(*) expand_readahead() [optional]
Called to allow the netfs to request an expansion of a readahead
request to meet its own alignment requirements. This is done by
changing rreq->start and rreq->len.
(*) clamp_length() [optional]
Called to allow the netfs to cut down a subrequest to meet its own
boundary requirements. If it does this, the helper will generate
additional subrequests until the full request is satisfied.
(*) is_still_valid() [optional]
Called to find out if the data just read from the cache has been
invalidated and must be reread from the server.
(*) issue_op() [required]
Called to ask the netfs to issue a read to the server. The subrequest
describes the read. The read request holds information about the file
being accessed.
The netfs can cache information in rreq->netfs_priv.
Upon completion, the netfs should set the error, transferred and can
also set FSCACHE_SREQ_CLEAR_TAIL and then call
fscache_subreq_terminated().
(*) done() [optional]
Called after the pages have been unlocked. The read request is still
pinning the file and mapping and may still be pinning pages with
PG_fscache. rreq->error indicates any error that has been
accumulated.
(*) cleanup() [optional]
Called when the helper is disposing of a finished read request. This
allows the netfs to clear rreq->netfs_priv.
Netfs support is enabled with CONFIG_NETFS_SUPPORT=y. It will be built
even if CONFIG_FSCACHE=n and in this case much of it should be optimised
away, allowing the filesystem to use it even when caching is disabled.
Changes:
v5:
- Comment why netfs_readahead() is putting pages[2].
- Use page_file_mapping() rather than page->mapping[2].
- Use page_index() rather than page->index[2].
- Use set_page_fscache()[3] rather then SetPageFsCache() as this takes an
appropriate ref too[4].
v4:
- Folded in a kerneldoc comment fix.
- Folded in a fix for the error handling in the case that ENOMEM occurs.
- Added flag to netfs_subreq_terminated() to indicate that the caller may
have been running async and stuff that might sleep needs punting to a
workqueue (can't use in_softirq()[1]).
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-and-tested-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Dave Wysochanski <dwysocha@redhat.com>
Tested-By: Marc Dionne <marc.dionne@auristor.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: linux-mm@kvack.org
cc: linux-cachefs@redhat.com
cc: linux-afs@lists.infradead.org
cc: linux-nfs@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: ceph-devel@vger.kernel.org
cc: v9fs-developer@lists.sourceforge.net
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20210216084230.GA23669@lst.de/ [1]
Link: https://lore.kernel.org/r/20210321014202.GF3420@casper.infradead.org/ [2]
Link: https://lore.kernel.org/r/2499407.1616505440@warthog.procyon.org.uk/ [3]
Link: https://lore.kernel.org/r/CAHk-=wh+2gbF7XEjYc=HV9w_2uVzVf7vs60BPz0gFA=+pUm3ww@mail.gmail.com/ [4]
Link: https://lore.kernel.org/r/160588497406.3465195.18003475695899726222.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161118136849.1232039.8923686136144228724.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161161032290.2537118.13400578415247339173.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161340394873.1303470.6237319335883242536.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/161539537375.286939.16642940088716990995.stgit@warthog.procyon.org.uk/ # v4
Link: https://lore.kernel.org/r/161653795430.2770958.4947584573720000554.stgit@warthog.procyon.org.uk/ # v5
Link: https://lore.kernel.org/r/161789076581.6155.6745849361504760209.stgit@warthog.procyon.org.uk/ # v6
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